The proposed experiments will employ electrophysiological and neuroanatomical methods to examine the manner in which the afferents from different sensory modalities are segregated in the developing superior colliculus of the golden hamster. Recent electrophysiological studies from this laboratory have suggested strongly that the terminal distribution of the spinal input to the colliculus expands dramaticaly following neonatal eye removal in this species. This work indicates that the precise laminar distribution of visual and extravisual inputs observed in the tectum of all mammals may not be the result of rigidly programmed patterns of synaptic connections but rather the end product of dynamic competitive processes operating during development. In the proposed experiments this possibly will be investigated further. Autoradiography and the anterograde movement of horseradish peroxidase in transected axons will be employed to delineate the terminal dstribution of the spinotectal tract in normal and neonatally enucleated hamsters and extracellular single unit recording, in these two groups of animals, will delineate the portion of the colliculus in which neurons receiving functional inputs from the spinal cord are localized. The results of these experiments, when taken together, should provide a relatively complete description of the organization of the spinal afferents to the tectum in normal hamsters and in animals subjected to the removal of one eye on the day of birth. Additional neuroanatomical studies will be carried out during development in both groups of animals in order to determine whether the postulated expansion of the terminal distribution of the spinotectal tract in the neonatal enucleates develops as a result of the active invasion of the superficial tectal laminae by the collaterals of spinal axons or because the removal of one eye in infancy interrupts the "retraction" of spinal terminals which at birth innervate all the layers of the colliculus.